Use of a Segmented Array Charge Coupled Device Detector for Continuum Source Atomic Absorption Spectrometry With Graphite Furnace Atomization

Abstract

A commercially available echelle spectrometer with a segmented array charge coupled detector (SCD) was used with a xenon arc lamp and graphite furnace atomizer for continuum source atomic absorption spectrometry (CS-AAS). Approximately 67% of the spectral wavelengths corresponding to the resonance transitions used for routine AAS determinations were available on the SCD. As many as eight elements were determined simultaneously with a read frequency of 50 Hz for each array. The high luminosity of the echelle and the high quantum efficiency SCD provided photoelectron levels that ranged from equivalent to 7 times higher than those previously measured by CS-AAS using a linear photodiode array (LPDA) detector. The low read noise of the SCD resulted in the absorbance measurements being limited by the photon shot noise of the continuum source. Detection limits were obtained that ranged from equivalent to a factor of 3 better than those previously obtained for CS-AAS and from a factor of 2 worse to a factor of 10 better than those for conventional, line source AAS. Sensitivities, as determined by intrinsic mass (mass necessary for an absorbance of 0.0044 pm s), were similar to those measured previously with an LPDA. The high resolution of the echelle allowed detailed inspection of the spectra surrounding the wavelength of the elements determined. Data were displayed using contour absorbance plots. Molecular peaks were observed within the spectral window of the sub-arrays for As (193.7 nm) and Se (196.0 nm). These peaks were spectrally and temporally resolved from the analyte peaks and disappeared in the presence of a Pd chemical modifier. A low sensitivity Pd line was identified that was 15 pm from the Se line. The Pd and Se peaks were resolved using a spectral bandwidth of 3 pm per pixel.